hansen



United States Patent HEATIN G FURNACE Fred A. Hansen, Chicago, Ill.,assignor to Lindherg Englilneermg Company, Chicago, 111., a corporationof Filed July 28, 1958, Ser. No. 751,300

1 Claim. (Cl. 219-35) This invention relates to a heating furnace andmore particularly to a furnace of the gas circulating type for treatingmetal articles and the like.

Heating furnaces of the gas circulating type have heretofore beenconstructed with heating elements mounted in the furnace side walls. Thecharge to be heated has been placed in a tubular liner within thefurnace and gas in the furnace was circulated over the charge and theheating elements by a fan.

With such furnaces a relatively large space must be left between theliner and furnace wall to accommodate the heating elements and access tothe heating elements for repair or replacement is very difficult. Moreseriously, heat is radiated from the elements to the sides of the chargeto result in uneven heating. Also gas flow over the elements is notuniform with the result that hot spots may develop and supply of currentto the elements must be limited to obtain satisfactory life. Theelements are also positioned where they are apt to be damaged duringloading and unloading of the furnace.

It is one of the objects of the present invention to provide a heatingfurnace which requires a minimum amount of floor space for a given sizeof furnace chamber and in which the parts are readily accessible forservicing.

Another object is to provide a heating furnace in which the heatingelements are mounted closely adjacent to the gas circulating means andare so positioned that gas flows directly and uniformly thereover fromthe gas circulating means to cool the heating elements uniformly.

According to a feature of the invention, the furnace is formed by ahollow base to receive the material to be treated and the heatingelements and gas circulating means are mounted in a removable cover forthe base. Preferably the gas circulating means is in the form of aradially bladed blower mounted centrally of the cover and the heatingelements are uniformly spaced around the blower closely adjacent to theblade tips for circulation of gas uniformly thereover at relatively highvelocity. Additionally the cover may carry a battle to confine the gasflow to a desired path and a control for the heating elements may beprovided on the cover, including a temperature sensing device mounted inthe gas stream between the cover and baffle.

According to another feature of the invention, the same cover may beutilized on bases of different sizes and may be removed from one baseand used on another while the charge in the first base is being cooledslowly.

The above and other objects and features of the invention will be morereadily apparent from the following description when read in connectionwith the accompanying drawing, in which:

Figure 1 is a vertical sectional view through a heat treating furnaceembodying the invention; and

Figure 2 is a horizontal section on the broken line 2-2 of Figure 1.

The furnace, as shown, comprises a base which may. if desired, bemounted in a pit or which may be mounted above the floor level. The baseis preferably cylindrical in shape with a circular insulated side wall10 extending vertically and closed at its bottom by an insulated bottomwall 11. The bottom wall may carry a plurality of spaced piers 12 formedof ceramic blocks, or the like, which may support a basket or the likeholding the charge, as indicated at 13, and which may also support ashell 14 spaced from the inner surface of the side wall to define adefinite path for gas flow.

The base terminates at its upper edge in a flat annular surface and ispreferably provided with an annular channel 14 open at the upper surfaceand adapted to contain a loose sealing material 15, such as sand, toprovide an effective seal for the cover. The base may be formed in anydesired manner, but is preferably formed ,of a metal shell 16 with aliner or filler of refractory material.

The base is closed at its top by a cover having a cylindrical insulatedside wall 17 which may be formed in a manner similar to the side wall ofthe base and which is substantially the same diameter. The side wall 17is adapted to rest on the top of the base side wall is formed with anannular projecting flange 18 which will extend into the sealing material15 to form a seal between the cover and base. Additionally, the covermay have a downwardly projecting annular flange 19 at its inner edge tofit within and against the inner shell 16 of the base side wall forfurther improved sealing.

The cover is closed at its top by a top plate 21 and an inner cover 22spaced below the top plate 21. The space between the plates 21 and 22may be filled with heat insulating material, such as refractorymaterial, if desired. The inner plate 22 curves downwardly in arelatively smooth curve adjacent to its periphery to terminate in theflange 18 so that air will be directed smoothly into the base therebyduring furnace operation. Preferably an annular baffle 23 is mounted inthe cover spaced from the plate 22 and curves downwardly at itsperiphery to terminate in a flange 24 which will fit over the sleeve 14when the cover is assembled on the furnace.

Air or gas is circulated in the furnace by gas circulating means shownas a blower having a plurality of radially extending blades 25 lyingbetween the plate 22 and the baffle 23. The blower rotor is mounted on ashaft 26 extending vertically upward through the central part of thecover and connected to a driving motor 27 on top of the cover. Theblower rotor may be made of any desired configuration such that when theblower rotor is turning it will draw air or gas upwardly through thecentral opening in the annular bafile 23 and will discharge the gasradially outward through the open space between the plate 22 and baflle23.

In order to heat the air a series of heating elements 28 are mounted inthe space between the plate 22 and baffle 23. As best seen in Figure 2,the elements 23 are uniformly and symmetrically spaced adjacent to thetips of the rotor blades 25 and around the rotor blades. The elements 28may be energized through leads 29 extending through the cover, as shown,and the temperature thereof may be controlled by a controller 31 mountedon the cover. The controller 31 includes a temperature sensing device32, such as a thermocouple or fluid filled bulb projecting into thespace between the plate 22 and baffle 23 anterior to the heatingelements in the direction of gas flow.

In operation, material to be treated, such as loose pieces or the like,may be placed in the basket 13 and dropped into the base, as shown, torest on the piers 12. The basket preferably terminates at or slightlybelow the top of the sleeve 14 so that it will not interfere withpositioning of the cover on the base. With the basket in place the covermay be placed on the base as shown in Figure l and the heating elementsmay be energized and the motor 27 started. At this time, the blower willcause a circulation of gas upward through the basket and the articlestherein outward over the heating elements, downward between the sleeve14 and inner shell 16 of the base, around the piers and up through thebasket and the material therein in a closed path. It will be noted thatthe heating elements are so positioned that the gas immediately uponleaving the blower fio-ws thereover at a relatively high velocity anduniformly over all of the heating elements. The heating elements maytherefore be operated at an extremely high current density withoutdanger of developing hot spots so that heating elements which are smallrelative to the power consumed thereby may be employed withoutshortening the life of the furnace. The controller 31 which isresponsive to the temperature sensed by the bulb 32 may maintain thepower input to the heating elements at the necessary level to produce adesired temperature within the furnace.

Upon completion of a treating operation the cover may be removed fromthe base and may be placed on another similar base containing a chargeof material to be trtated. Where it is desired to allow the material tocool slowly a blank cover such, for example, as a fiat sheet of heatinsulating refractory may be placed over the base. this way a singlecover can serve a large number of bases which may be of the same ordiflerent sizes by varying the vertical height thereof. Furthermore,since all of the operating parts are in the cover itself they arereadily accessible for servicing without the necessity of tearing down acomplete furnace.

Since the space between the shell 14 and the inner wall of the base iscompletely unobstructed it may be made of minimum width to accommodatethe desired volume of gas flow so that the furnace may be made ofminimum size for a given capacity. The charge will be heated uniformlyby substantially pure convection which is highly desirable. What littleradiation heating does occur is at the top of the charge where itcompensates for the heat loss through the cover which normally existsand helps to heat the top of the charge which is normally the last partto heat.

While one embodiment of the invention has been shown and describedherein, it will be understood that it is illustrative only and not to betaken as a definition of the scope of the invention, reference being hadfor this purpose to the appended claim.

What is claimed is:

A heating furnace comprising a hollow base open at its top, a liner inthe base spaced from the side wall and above the bottom thereof andterminating substantially level with the top of the base, means wit inthe liner to support articles to be heat treated for circulation of gastherethrough, a cover fitting detachabty on the base, and closing theopen top thereof, a gas circulating unit carried by the cover above thetop of the liner to circulate heated gas radially outwardly in the coverand in closed circuit downwardly between the liner and base and upwardlythrough the liner and over the articles therein, heating elementscarried by the cover around the circulating unit in the path of thecirculating gas to heat the gas, and an annular baffle carried bythecover underlying the gas circulating unit and heating elements andhaving a central opening registering with the gas circulating unit and adownturned peripheral flange telescopically interfitting with the top ofthe liner to confine the circulating gas to said closed circuit.

References Cited in the file of this patent UNITED STATES PATENTS1,721,840 Smith July 23, 1929 1,827,194 Grothe Oct. 13, 1931 1,986,088Wild Jan. 1, 1935 1,996,680 Lobley Apr. 1, 1935 2,376,174 Munninget alMay 15, 1945 2,412,103 Spooner Dec. 3, 1946 2,523,796 Weeks Sept. 26,1950

